Extrusion of articles

ABSTRACT

An extrusion control system for use with one or more extruders has a data acquisition module in communication with one or more data acquisition nodes that are associated with an extrusion process. A control module is also in communication with one or more control nodes associated the extrusion process. A synchronization signal to one or more control nodes causes the nodes to adjust to a predetermined setting.

TECHNICAL FIELD

This invention relates to methods and apparatuses for making extrudedarticles, and more particularly to methods and apparatuses for makingextruded articles having varying cross-sections and materials usingclosed-loop control.

BACKGROUND

Many articles today are made using extrusion processes. Extrusion isgenerally a continuous process whereby a material, such as athermoplastic, is conveyed in a melted form through a die that has adesired cross section. The material exits the die and quickly cools intoits final, solid form. Thus, extrusion is an effective continuousprocess for making products such as tubes, films, piping,weather-stripping, window frames, and other articles having a constantcross-section. For such articles, the extrusion process is efficient,convenient, and can run continuously to produce high volumes of product.Extrusion differs from discontinuous batch processes such as injectionmolding, that make single, separate articles, and can produce articleshaving complex shapes without much effort.

Articles that vary in their material composition or in thecross-sectional shape may also be produced via extrusion, however. Forexample, the cross-sectional diameter of a tube may be varied by varyingthe air pressure introduced into the interior of the tube as it leavesthe extruder die. Also, the materials being fed to the extruder may bechanged in process or in situ if different parts of an article requiredifferent material properties.

The extrusion of discontinuous articles is much more complicated thancontinuous extrusion of constant cross-section and constant materialarticles. Articles formed by continuous extrusion may generally beproduced by establishing the production parameters throughtrial-and-error when an extrusion line is first started. The extrudermay then be operated continuously with little attention from theoperator, except for infrequent and minor variations and corrections.The material that must be discarded during the initial set-up andcalibration is generally very small in relation to the total productproduced. On the other hand, the conditions in a discontinuous extrusionsystem are, of necessity, always changing. As a result, varioustransient conditions can encroach on the production process. Theseconditions must be accounted for before the article of interest exitsfrom the extruder system. And because the percentage of wasted materialis best kept to a minimum, the slow, trial-and-error calibration methodis generally not appropriate for discontinuous extrusion operations.Moreover, it can be difficult to produce quick transitions in materialsor in the extrusion geometry. These difficulties in producing asatisfactory discontinuous article by extrusion are compounded when thearticle being produced has extremely tight tolerances (whether forgeometry, materials, or performance). The problems are furthercompounded over time as a system operates, because the various systemparameters may each drift away from their appropriate set points.

As one example, angioplasty balloon catheters may be produced in part orin whole by extrusion. Such catheters are generally comprised of asmall, flexible, but strong, hollow plastic shaft, with an expandableballoon mounted at its distal end, along with a tapered, flexible tip.The catheter must generally be capable of being threaded through avessel or artery so that the balloon may be placed at a site in thepatient, for example, where there has been arterial stenosis. To providethe required combination of flexibility and strength, it may benecessary to form different parts of the catheter out of differentmaterials that have different degrees of compliance, or softness, withina single catheter assembly. It may also be preferable to form a singlepiece possessing gradual, consistent, property transitions instead ofproducing multiple pieces and then joining them together, such as bysonic welding or with adhesive bonding. Improved profile dimensions mayalso be achieved by forming the balloon with its tapered tip in the sameprocess as the balloon and the shaft. Each of these steps requiresdiscontinuities in the material leaving the extruder, whether in termsof material or geometry, and creates difficulties in controlling theextruder output.

Systems that simply monitor processing variability and react to maintaina desired part dimension are generally inadequate to produce articleshaving discontinuities and very tight tolerances, where numerousindependent process parameters can affect numerous attributes of thearticle. As a result, there is a need for a system and method thatprovide accurate control over a discontinuous extrusion process.

SUMMARY

In general, a device and method for producing extruded items isdisclosed. The items may be made up of a plurality of repeating ornon-repeating parts that may be separated into individual parts afterbeing extruded. In producing the items, the device may be equipped witha control system that repeatedly resynchronizes one or more of thecontrol points that control the extruder operation.

In one embodiment, an extrusion control system for use with one or moreextruders is disclosed. The system comprises a data acquisition modulein communication with one or more data acquisition nodes that areassociated with an extrusion process, a control module in communicationwith one or more control nodes associated the extrusion process, and asynchronization signal generator that generates a synchronization signalfor the one or more control nodes to cause the one or more control nodesto adjust to a predetermined setting. A part profile, which may comprisea representation of the outer diameter of an extruded part (including aminimum specified part profile and a maximum specified part profile),may also be provided that corresponds to the extruded part to beproduced by the one or more extruders. The synchronization signalgenerator may generate a synchronization signal at a substantiallyrepeating period, such as a period that is a function of the length ofthe extruded part, including by being generated for each part. A firstevent marker (which may correspond to the beginning or the end of a partprofile) may also be provided in association with the part profile,whereby the synchronization signal generator generates a synchronizationsignal when the system encounters the event marker. The data acquisitionmodule and the control module may each be in communication with acomputer that monitors and controls the operation of the one or moreextruders. The computer may have a display that presents an image of thepart profile.

The synchronization signal generator and the signal itself may take avariety of forms. The generator may communicate with each of the one ormore control nodes over a dedicated communication channel or a sharedcommunication medium, and the synchronization signal may comprise asynchronization pulse. The system may also comprises a velocity sensorthat allows the velocity of an extruded article to be measured, and adata acquisition node having a laser gauge that acquires data relatingto the outside diameter of an extruded article produced by the extrusionprocess. The control module may also be in communication with a PIDcontroller associated with a variable speed drive for the extruder, bywhich the synchronization signal causes the PID controller to return toa preset speed. The control module may also carry out a PID controlsequence after the synchronization signal generator generates thesynchronization signal, and the control module may communicate withcontrol nodes on more than one extruder, such as by causing a switchoverform a first material in a first extruder to a second material in asecond extruder. The control module may also be in communication with asizing air device controller associated with an extruder, so that thesynchronization signal may cause the sizing air device controller to setto a predetermined value. A reporting module may provide data acquiredby the data acquisition modules.

In another embodiment, a method of producing an extruded articlecomprised of a plurality of extruded parts is disclosed. The method maycomprise the steps of defining a part profile, associating a pluralityof control parameters with the part profile, wherein each controlparameter has an initial value, producing a first extruded part usingthe plurality of control parameters in a closed-loop control system,resetting each of the plurality of control parameters to its initialvalue, and producing a second extruded part using the plurality ofcontrol parameters in a closed-loop control system. The resetting stepmay comprise sending a synchronization signal such as a pulse to aplurality of control nodes. The signal may be transmitted on a dedicatedcommunication path, and may be sent after the first extruded part isproduced but before the second extruded part is produced.

In yet another embodiment, an extruded article is disclosed. The articlecomprises a plurality of extruded parts, a plurality of materialtransitions, wherein each part contains at least one materialtransition, and wherein the material transitions are each shorter than0.25 inches in extruded length. The article may include more than 30 ormore than 50 extruded parts.

A plurality of extruded parts produced as part of a substantiallycontinuous extrusion process is also disclosed. The parts have a firstsection on each of the plurality of extruded parts having a constantoutside diameter; a second section on each of the plurality of extrudedparts having an increasing outside diameter, wherein the outsidediameter of the first section of each of the plurality of extruded partsis substantially identical to the outside diameter of the first sectionof each of the other extruded parts; and wherein the outside diameteralong the second section of each of the plurality of extruded parts issubstantially identical to the outside diameter along the second sectionof each of the other extruded parts. The outside diameter of the firstsection of the first extruded part may differ from the outside diameterof the first section of any other of the plurality of parts by no morethan 0.0010 or no more than 0.0005 inches.

An extruded catheter is also disclosed, comprising a catheter tip madeof a first plastic material, a balloon having an expanding portion, amiddle portion, and a contracting portion, and a catheter shaft defininga lumen connected to the contracting portion, wherein the catheter shafthas a transition zone smaller than 0.25 inches in which the cathetershaft transitions from the first plastic material to a second plasticmaterial.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an extrusion control system.

FIG. 2 shows graphically a comparison of extrusion process inputs and acorresponding extrusion process output.

FIG. 3 shows a display that may be provided to the operator of anextruder

FIG. 4 is a flow chart showing a procedure for initiating an extrusioncontrol system.

FIG. 5 is a flow chart showing the general operation of an extrusioncontrol system.

FIG. 6 shows a profile of a medical balloon catheter that may beproduced by an extrusion process.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an extrusion control system 10 capableof controlling the operation of one or more extruders. In general,system 10 is provided with controls that allow it to produce an articleof varying performance properties or dimensions, which may be referredto as a discontinuous article, using a continuous or substantiallycontinuous extrusion process. System 10 is connected to extruder 12 thatreceives material, such as thermoplastic pellets in a solid form, meltsthe material, and conveys the material through a die to form an extrudedarticle 14. Extruder 12 may be adjoined to one or more other extruders(not shown) in the die region in a multi-extrusion or co-extrusionsystem, whereby each extruder is loaded with one raw materialcomposition, and the system 10 may be switched over in-process from onematerial to the other.

Extruded article 14 may be comprised of a plurality of extruded parts15, which may be obtained by cutting article 14 into discrete sectionsafter it has been extruded. Extruded parts 15 may be repeated matchingparts, such as medical balloon catheters. Also, extruded article 14 maybe cut into parts after each part exits extruder 12. In this manner, thevarious parts that form an article can be produced in a continuousprocess, and then may be cut apart for further processing or use.

System 10 may control extruder 12 using computer 16. Computer 16 mayobtain information regarding the operation of extruder 12 through dataacquisition module 18, and may provide signals to operate extruder 12through control module 20. Although data acquisition module 18 andcontrol module 20 are pictured as separate modules lying outsidecomputer 16, and connected to computer 16 by separate data paths, theycould be connected to a common bus, and could be components insidecomputer 16, such as expansion cards, or could be integrated withcomputer 16. The modules could also be integrated with each other as asingle hardware or software module. In particular, the interfacesbetween computer 16 and extruder 12 can take any of a variety ofappropriate forms, as understood by a skilled artisan.

Data acquisition module 18 may be connected to a variety of sensors orother devices for determining the current status of extruder 12 orextruded article 14. For example, extruded article 14 may pass through acooling device 22 after exiting extruder 12, and the temperature andlocation of cooling device 22 may be monitored. Laser gauge 24 may beprovided near the exit of extruder 12 to generate a signal that allowsthe outer diameter of the extrudate to be determined. A second lasergauge (not pictured) may also be provided (either separately from, orcombined with, laser gauge 24) to allow for the measurement of ovalityof the tube. Durometer 26 may be provided to allow for the measurementof hardness of the extruded article 14. In addition, laser velocitygauge 28 may be provided to allow for the measurement of the extrudedarticle's velocity. Data may also be acquired from mechanical pullingdevice 30, which grips extruded article 14 and maintains a controlledamount of tension on article 14. Other data acquisition devices may alsobe used, including devices using ultrasonic and magnetic resonanceimaging (MRI) technologies.

Data acquisition module 18 may be used to aggregate data that iscollected by the various sensors or other devices. For example, one ormore of the devices may be configured to obtain data at a very high rateor granularity, such as by 2833 scans per axis per second by laser gauge24. If multiple devices are connected to computer 16, each with veryhigh data acquisition rates, computer 16 may be incapable of digestingall of the data simultaneously while also communicating with controlmodule 20, or may have no need for all of the data. Thus, each devicemay process the data it receives, and pass a subset of that data or amore compact representation of the data (such as an average of samplesover wider sampling periods) to data acquisition module 18.Alternatively, data acquisition module 18 may receive all sampled datafrom a device and then process the data before forwarding it to computer16.

Control module 20 receives signals from computer 16 and communicateswith various nodes that may control extruder 12. For example, controlmodule 20 may send signals through line 50 to a variable speed drive ora stepper motor 32 that is part of extruder 12. Control module 20 alsomay generate signals and send them via line 52 to modulate a heater 34of extruder 12. Control signals may also be sent to sizing air device 36via line 54 to regulate the air pressure that is introduced into theinside of extruded article 14, and thereby control the inner diameter ofarticle 14. The inner diameter of the article may be controlled byadjusting the relative speeds of the extruder 12 and pulling device 30,such as by sending control signals through line 56. The devices thatreceive signals from control module 20 may take any of a variety offorms that are well known, and may comprise multiple servo motors orother control mechanisms connected to the system.

Data may be transferred between data acquisition module 18 and computer16 by data bus 46. Likewise, information may be transferred betweencontrol module 20 and computer 16 by control bus 48. Alternatively, databus 46 may be positioned between data acquisition module 18 and the dataacquisition nodes, and control bus 48 may be positioned between controlmodule 20 and the control nodes. For example, data acquisition module 18and control module 20 may each be connected to a SCADA bus, such as anEthernet network (either shared or switched) and communicate with theirrespective nodes over that network. Moreover, multiple extruders may beconnected to a single computer, either with one control module and onedata acquisition module for each computer, or one control module and onedata acquisition module for each extruder, or by other appropriatearrangement. A single bus or network may be used for the communication,or multiple buses or networks may be used, as appropriate, for theparticular application.

Computer 16 may be any structure that provides an operating environmentsuitable for implementing the techniques described in this application.For example, computer 16 may contain a processor connected to systemmemory (including ROM and RAM) through a bus controller and a systemdata/address bus. Computer 16 may be any server, personal computer,laptop or even a battery-powered, pocket-sized, mobile computer known asa hand-held PC or personal digital assistant (PDA). Computer 16 may alsoconnect to other devices, such as a video adapter and display, internalor external fixed disk, floppy disk, optical or tape media, and modem,keyboard, mouse, or microphone.

In addition, data received by computer 16 or generated by computer 16may be stored in database 42, including acquired data (such as measuredparameters of the extruder 12) and process data (such as informationregarding particular articles that are to be manufactured using extruder12). Computer 16 may also be connected to a network 44 that is separatefrom, or combined with, the network by which computer 16 communicateswith extruder 12. This network 44 may include a corporate intranet orthe Internet. In this manner, computer 16 may communicate informationabout the performance of the system with other computers, includingcomputers at remote locations, and may also receive information, such asrecipe information that specifies the various parameters of a part to beextruded by system 10.

Synchronization bus 40 may also be provided between control module 20and its related nodes. Synchronization bus 40 may carry asynchronization signal to cause one or more of the control nodes to setthemselves to a particular value. For example, each node may have apreset starting value for its operation, and a signal on synchronizationbus 40 could cause the nodes to each begin operating anew from thatpreset starting value. The synchronization signal may help alleviateproblems of drift that arise in the use of control systems, particularlywhere multiple different parameters are being controlled simultaneously.In particular, the various process parameters may all be arranged sothat the system is producing a desired output, but each node may be at apoint, especially when combined with each of the other nodes, at whichthe system as a whole is very unstable, and small variations in one ormore inputs could have a major impact that would negatively affect thecharacteristics of the article in an appreciable manner. Thesynchronization signal allows the various inputs to be set to valuesthat can be expected to provide accurate and stable control of theprocess output. Although synchronization bus 40 is shown in the figureas a dedicated communication line, the synchronization signal could alsobe sent on a network that carries other communications between controlmodule 20 and the controlled nodes, or in any other appropriate manner.In addition, the synchronization signal may take any of a variety offorms, such as an electrical pulse, a combination of signals, or aappropriate multi-bit representation that is recognized by the nodes asa indication that resynchronization should occur.

An example of the operation of the synchronization signal may provide abetter understanding of the signal value to the system. In operation,each of the control nodes generally adapts to various conditions that it“sees,” so that although that node is maintaining a desired output atany given moment, it may have drifted far enough from its set point thata small change in conditions will cause the system to be unable tomaintain its desired output. As an example, sizing air device 36 may berequired to produce a certain inner diameter for extruded article 14,and may need to maintain a particular pressure within extruded article14 to do so. To produce that pressure initially, sizing air device 36may need to be provided with a particular starting voltage, and thatvoltage may need to be altered as production continues to furthermaintain the pressure. After a time, the voltage applied to sizing airdevice 36 may be substantially different from the starting voltage thatwas needed to maintain the desired pressure. Although the modifiedvoltage may currently be providing the appropriate pressure, whencombined with all the other surrounding factors that affect thecomposition of extruded article 14, the present voltage may make for arelatively unstable system. By causing the various nodes to return totheir start values, the synchronization signal can return the entiresystem 10 to a point of known stability at which the extruded article 14meets its intended specification.

Where the system is set up to produce a number of repeating parts 15,the synchronization signal may be timed to reset the various controlnodes near the transition from one part 15 to the next. In this manner,any transient change in the any measurable attribute of the extrudedarticle 14 (such as a step or near-step increase or decrease in itsouter diameter) will occur in an area that is non-critical and thatcould be separated and discarded when the parts 15 are separated out ofthe extruded article 14. Such a periodic synchronization signal may alsoimpart a degree of repeatability for the various attributes of theparts. In particular, the point in the production of each article atwhich the synchronization signal is provided, or some point a knowndistance from that point, may be used as a base from which to identifyand compute various attributes for each part. For example, geometrytransitions such as tapers, may be measured from the base point for eachpart, thereby eliminating any accumulated error across multiple parts inidentifying the position of extruded article 14. As a result, thelongitudinal alignment of each part may be closely determined, and maybe used to improve the degree of control over the various attributes ofeach part.

FIG. 2 shows diagrammatically a comparison of extrusion process inputsand a corresponding extrusion process output in comparison to the use ofa synchronization signal. This diagram is intended to provide a visualexample of the manner in which the synchronization pulse could affectthe repeatable production of an extruded article. The x-axis in thefigure represents elapsed time, while the y-axis represents thedeviation of each parameter from its norm (where each norm isrepresented by a horizontal line). Each input parameter can beassociated with a particular device that works with the extruder, suchas a motor affecting extrusion speed, heaters for the extruder, apulling device, or an air sizing device.

Two vertical lines, P1 and P2, represent times at which synchronizationsignals are sent to one or more of the control nodes. Thesynchronization signals cause each device to return to its normal valueand continue its operation from that normal value. Thus, over time, theoperating values of the various inputs can vary and drift from theirnormal values. Because the interrelationships between the various inputscan be very complex, the drifts might simply cancel each other out or,alternatively, they could amplify each other. In the former case, thevarious drifts would have little or no effect on the output, while inthe latter case, there would be a severe effect on the output. However,as each of the devices drift father from their respective norms, thelikelihood that the output will be noticeably affected increases, andthe system will become more unstable. Thus, the synchronization signalmay be generated at the appropriate time even if the output is stillgood, to ensure that the system does not enter a point at which theoutput could quickly become bad.

The synchronization signals reduce the danger that the drifts willreinforce each other, because the signals cause each input to return toa normal value which is understood to produce a proper and relativelystable output when the other inputs also return to their normal values.The synchronization signals may be generated at any appropriateinterval, such as once for each produced part.

FIG. 3 shows a display 100 that may be provided to the operator of anextruder. In a center window 101, a profile of an article, such as aballoon catheter, is displayed. As shown, parameters of the articlechange at particular points so that, for example, the article may beproduced as a single part having varying diameter. The profile is shownas two cross-section edges for a generally cylindrical object of varyingdiameter. The outer radius as viewed from the top or bottom of thearticle is represented by two x-dimension lines 102, 104, which,respectively, represent the maximum and minimum specified radius for thearticle in the x-dimension. The outer radius as viewed from the sides ofthe article is represented by two y-dimension lines 106, 108, which,respectively, represent the minimum and maximum specified radius for thearticle in the y-dimension. These lines thus provide a visual cue to theoperator during the production of the article regarding the expecteddimensions of the article, and when read together, they provide anindication of the ovality of the article. As the production occurs,tracking lines 110, 112 are provided on display 100 and correspond tothe actual radii of the article as it exits the extrusion die, asmeasured by laser gauges or other instruments. These lines thereforeprovide the operator with an indication of the actual progress of theextrusion, as compared to the expected and specified parameters. Whilethe tracking lines 110, 112 as shown in the figure move from left toright across the screen in the figure as the article exits the die, thetracking lines could be produced at a constant vertical position on thescreen, and the dimension lines 102, 104, 106, 108, could scroll fromright to left across the screen as each part is produced, or thetracking lines could move from right to left, or the progress of thepart could be shown in any appropriate manner. Also, other processparameters, such as a durometer reading, an indication of ovality, or anindication of wall thickness, could be provided to the operator eithernumerically or graphically in a similar manner. Moreover, the trackinglines 110, 112 or other displayed parameters may be displayed as movingdots or short moving lines, rather than as lines that span display 101.The displayed size of the article shown in window 101 could also becontrolled and varied.

Several vertical lines in display 101 represent time-based occurrencesrelating to the extrusion. For example, control output line 120 mayrepresent air output control. Event markers 118 delineate “events” thatbring a distinct change in the operating parameters of the extrusionprocess. For example, an event may mark a change in any relevant productattribute, such as material, size, coating, or elongational properties,or in a combination of attributes. Also, an event may represent thestart of a geometric change in the article, such as an intended increasein outside diameter (as indicated by all but the right-most event marker118). The event can also trigger more complex changes. For example, theevent can trigger a PID control sequence, such as an increase in sizingair pressure that results in a taper in the extruded article. Also,display 101 may be arranged so that the operator can click on or touch aparticular event marker 120 and be presented with control information,such as in a pop-up window, associated with the event, such as variousPID parameters. Multiple PID loops may be used with regard to a singleline, and other modes of control may also be employed. The PID controlmay also be a forward-looking PID.

Other areas of display 100 provide other information related to theextrusion process. For example, file view box 124 shows the name of thepart currently being produced, by showing a recipe name and certaindimensions of the article. The box 124 may contain the names of multipledefinition files to which the system has access. The operator mayhighlight a particular file, or may touch the screen or click on thefile name to load a particular file that contains information on theprocess parameters for a particular article, and to produce theinformation shown elsewhere on display 101. Description area 126provides information relating to the particular manufacturing run, suchas the name of the machine (or extruders) on which the run is performed,the product name or number, and a lot number. For example, the machine(i.e., particular extruder or extruders) for which the profile andrecipe were established may be shown, the product number or descriptorto be produced from the file may be indicated (so that the operator canconfirm that the appropriate file is being used), and the particular lotnumber may also be provided. One or more of the entries in thedescription area 126 may be edited, and the information in thedescription area 126 may be stored for later retrieval or may beassociated with other data. For example, an operator may call up a file,change the description of the product, and produce a group of articlesthat receive a lot number automatically generated by the system orretrieved from a central system. That information may then be stored ina log file or other appropriate file, along with other information aboutthe production of that lot (such as the data acquired during production,the number of articles produced, the date, etc.), and may be lateraccessed, such as to troubleshoot problems with the articles that areproduced, or for analysis, such as by using statistical process controltechniques.

Although window 101 is shown as displaying data relating to an x-axisradius and a y-axis radius, it could also display the various parametersand attributes of the extrusion process and the extruded article in anyother appropriate manner. For example, an “axis” view could be providedto show the cross-section of the article as it is produced. Thus, theaxis view might show a pair of concentric circles that represent theminimum and maximum specified diameters for an article at a particularlocation. Also a side view of a part could also be displayed. Such aview would look similar to that shown in FIG. 3, but the upper profilelines would represent the radius of the article above its centerline,while the lower profile lines would represent the radius of the partbelow its centerline. Such a view would thus present a sidecross-section of the article.

Other display controls (not shown) could also provide additionalfunctionality in the operation of display 100. For example, buttons maybe provided to allow an operator to change the current view that ispresented in window 101. Controls may also be provided to allow a userto load or save information regarding an article or a particularproduction run. For example, the user may load a selected profile andrecipe, and may save the profile or recipe if changes have been made toit. Additionally, the user may save data that has been collectedrelating to a particular run of the machine. The user may also exit fromthe application, such as to shut the system down or to switch to anotherapplication. The system may be integrated as part of a windowedoperating system so that the user can also switch easily to otherapplications without exiting display 100.

Also, display 100 may be configured to allow a user, such as a designeror engineer, to build or modify an article profile on-screen. Forexample, the user could draw particular profile lines and establish ormodify event markers interactively on display 101. The user could alsobe provided with a worksheet into which the user could enter datarelating to each discrete segment of an article. Alternatively,information for defining the recipe and profile of an article can beimported from another design program or from an appropriately-formattedfile, such as over a network or removable media.

Display 100 may also provide controls to allow a user to configureparticular data acquisition devices. For example, the user may be givengraphical controls to select particular features associated with a laserdiameter gauge, such as the communication port and communication ratefor the diameter gauge. The user may also adjust operating parameters ofthe device such as whether the laser gauge measures across the articlein one or multiple dimensions, whether the values displayed (which aregenerated as an average of all the samples taken over a particular timeperiod) are averaged over the sampling time or over all the number ofsamples, the number of samples made per second, and the frequency of thesamples used in computing the average.

Display 100 may also allow a user to tune certain parameters of thevarious control nodes associated with an extrusion control system. Forexample, the inner diameter sizing air device on an extruder may requirea particular control sequence to create an extrusion having an innerdiameter that changes from one value to another. This control sequencecan be associated with an event marker and can be established by settingthe various PID parameters in a manner known to those skilled in theart. Also, the operator may wish to alter certain parameters while theprocess is occurring, for example, if the system shows that the processis repeatedly operating outside of desired ranges.

FIG. 4 is a flow chart showing a procedure for initiating an extrusioncontrol system. The system may be established to produce discontinuousarticles according to a “recipe” of materials and a profile template.For example, in the case of a balloon catheter, the profile template mayrepresent the cross-section of the catheter from the tip, across theballoon, and along the catheter shaft, and could take into account theinside diameter, the outside diameter, and various durometers along thelength of the part, and the specific length of each portion of thecatheter. The recipe for the catheter could represent the proportion ofmaterial from each extruder in a co-extrusion that is to be provided foreach portion of the catheter. At step 200, the system is first started,such as by resetting, initially turning it on, or otherwiseresynchronizing the system. The system at first initializes, by readingfrom its memory, the values for the recipe and profile associated with aparticular article, such as the last article that was produced by thesystem (step 202). The operator of the system may then be given theopportunity, at step 204, to produce articles according to the storedprofile, to select another stored profile (whether stored within thesystem or elsewhere), or to enter the parameters for a new profile. Ifthe operator selects the stored recipe and profile, the system providesa display on the operator's screen that corresponds to that profile andrecipe. If the user chooses not to use the stored recipe and profile,the system provides the operator, at step 206, with the opportunity toselect another stored profile or to enter the parameters for a newprofile. The parameters for a stored profile may have been enteredearlier by the user, may be accessed from another computer where theparameters were defined, or may be extracted from other data, such asthe data of a CAD/CAM system. After the operator has selected or entereda desired recipe and profile, the system loads the recipe and profile atstep 208 and displays it to the operator at step 210. The operator maythen continue with the selected part, may modify the profile or recipe,or may select a different part to produce. Once the operator chooses togo on-line with the production of the articles at step 212, the systemstarts its closed-loop control at step 214 and begins operating theextruder or extruders.

FIG. 5 is a flow chart showing the general operation of an extrusioncontrol system. In general, this flow chart shows steps that may befollowed by the system once the closed-loop control discussed withrespect to FIGS. 2-4 has begun. Initially, at step 240, a recipe andprofile are established for a particular article or articles. For eachlocation along the length of the article, the various parameters, suchas melt pump speed and wall thickness, may have either preset orcomputed values. For example, the inner diameter of a tube may have aset value where the diameter is constant along the article's entirelength, and may have a computed value where the outer diameter istapering. Therefore, at step 242, for each sampling or control interval,values of the relevant parameters are read from the various dataacquisition nodes, and signals may be sent to the various control nodesin the system. The control interval could be separate and different forreceiving data as it may be for sending control information, and eithersampling interval may be set for an appropriate length of time. Forexample, in the production of medical catheters, a sampling interval of1-10 milliseconds per sample may be appropriate.

At step 244, the system checks to determine whether there has been areset condition, such as an operator-induced interruption of theproduction process or a shut-down of the control system. If there hasbeen a reset, the system may return to the parameter values of thecurrent recipe and profile, or may conduct a process like that shown inFIG. 4 to obtain the operator's desired recipe and profile.

A synchronization signal is provided at step 246. As an example, astandard network reset signal may be directed to the data bus, to thecontrol bus, to both, or to any other communication medium in thesystem. The signal may be provided at a periodic basis (such as everyseveral seconds), upon the occurrence of a particular process event(such as the completion of a distinct article), or upon the occurrenceof a particular process value (such as a value of a parameter ormultiple parameters that indicates a system fault). The signal may besent over the data bus or the control bus, or it may be sent over itsown communication lines. When the signal occurs, the system returns tousing the stored parameters for the recipe and profile of the articlebeing produced, as shown by step 248. In some cases, a synchronizationmay produce a sudden step, or discontinuity, in these cases, it ispreferable to do so within the discard section of the software.

At step 250, the process encounters an event marker that indicates theprofile or recipe (or some other parameter) of an article needs tochange. At this step, the system returns to the profile or recipedefinitions to obtain the needed parameters for the extrusion process.The system may then read the new values and adjust the set points forany relevant parameters accordingly, as shown at step 252.Alternatively, if no event marker is encountered during a relevantsampling or control interval, the system may simply continue operation,such as by using existing constant parameters or by calculating newvalues for changing parameters (such as the article diameter, where thearticle is tapering). In addition, the set points may be continuallyadjusted to maintain the appropriate output for the system.

FIG. 6 shows a profile of a medical balloon catheter 280 that may beproduced according to the disclosure above. The catheter 280, as shown,has been severed from other catheters on each of its ends, but wouldnormally be made as part of a continuous, repeating article in anextrusion process. The catheter 280 is also comprised of a number ofdistinct sections. Catheter 280 may have a first geometric section 282having a constant inside and outside diameter, followed by a secondgeometric section 284 having an increasing diameter from left to right,and a thinner wall thickness than the thickness of first geometricsection 282. The wall thickness may be reduced, for example, byproviding additional tension on the string of catheters, such as by amechanical pulling device, while they are being extruded. A thirdgeometric section 286 of constant diameter and having a thin wall isfollowed by an fourth geometric section 288 of decreasing diameterhaving a thin wall. The relatively thin wall in sections 284, 286, and288 allow those sections to expand more easily than the rest of catheter280, and thus to form a balloon area in catheter 280. A fifth geometricsection 240 has a constant diameter and thickness, and has a section ofchanging composition 296 in it. Thus, the composition of the plastic tothe right of section 296 is different from the composition of theplastic to the left of section 296, and section 296 comprises atransition area in which the two plastics are mixed. For example, theplastic to the right of the transition may be less pliable than theplastic to the right, so that the main shaft of the catheter may bepushed through passages to get to the desired location during a medicalprocedure.

The system and methods described above permit precision andrepeatability in the production of discontinuous parts in a continuousextrusion process. In particular, the resetting of certain parameterswith each part provides a predictable measuring point from which to basethe operation of the control nodes. It also removes inherent error andinstability that may build up during the operation of a closed-loopsystem having multiple input variables. Thus, for example, the systemand methods described above are capable of producing extruded articles,both straight and tapered, with cross-sectional control to 0.0005 inchesand below, and allows continuous, on-line characterization of extrusionattributes.

In addition, the system and method produce extruded articles that havevery repeatable property transitions. In other words, propertytransitions on the one-hundredth part produced in a continuous processwill be substantially the same as the property transitions for the firstpart. For example, the system and method can produce repeatable changesin material hardness (durometer), material surface tactilecharacteristics, and material molecular structure orientation.

The system and method may also achieve very repeatable placement onextruded parts of features external to the extruder. That is becausesuch external operations may also be keyed to the location of a basepoint that is reset periodically, such as for each part. For example, inproducing a medical balloon catheter, repeatable placement of markerbands, stents, and material coatings may be achieved. Also, variation inthe length of parts may also be minimized, such that the cut length ofthe parts produced in an extrusion process would vary from each other byless than 0.1 percent, i.e., a ten inch part can be repeatably cutbetween 9.99 inches and 10.01 inches.

EXAMPLES Example No. 1 Production of an Extruded Article of VaryingCross-Section

A material hopper of an extrusion apparatus, such as a positivedisplacement apparatus, is filled with Pebax 7233 nylon. The apparatusis started, and plastic begins to exit from the diehead. The diehead hasa conical outer ring and an inner tip, positioned so as to create acylindrical tube of material. The outer ring has an inner diameter of0.0770, and the outer edge of the inner tip is spaced from the outerface of the outer ring by 0.002 inch.

The initial material to exit from the polished spiral diehead is acylindrical tube, and forms a catheter balloon blank. The temperaturesof the apparatus are set as follows: Feed Liner  80° F. Barrel - Zone 1300° F. Barrel - Zone 2 335° F. Barrel - Zone 3 360° F. Barrel - Zone 4360° F. Clamp 360° F. Filter 360° F. Melt Pump (lcc/rev) 360° F. Diehead370° F.Other parameters of the apparatus are set as follows at start-up: meltpump rpm 75.02; puller speed 22.10 rpm; extruder speed 4.65 rpm; tankgap 0.1146 inches; water dam diameter 0.089 inches; screw ¾ inch; airpressure 3 inches of water.

When material exits the die, it is strung through a waterbath, an ultrasonic gauge, a vacuum wipe, and an o.d. gauge, and then passed over aspeed laser and into a puller. The material then passes through acutting device to a blowoff conveyor. The control system is started oncethe initial line is strung. Once started, the system receivesmeasurement data from the online measuring devices, and auto loopadjusts air, puller speed, extruder rpm, and meltpump rpm (or anycombination of these parameters) to maintain the product exiting the dieat the intended parameters. A synchronization pulse is sent to eachdevice that needs to synchronize at an interval of once per part.

The resulting catheter has the following dimension and tolerances:length of 13 inches ±0.020 inches; i.d. of 0.0215 inches; o.d. of 0.0395inches; wall of 0.0090 inches. Each of the i.d., o.d., and wallthicknesses have tolerances of less than or substantially equal to0.0003 inches.

Example No. 2 Production of an Extruded Article With Different Materials

A first hopper of a co-extrusion apparatus, such as a positivedisplacement apparatus, is filled with LDPE (Plexar) to act as the tielayer. A second hopper of the apparatus is filled with HDPE (Marlex) toact as the inner layer, and a third with Nylon 12 such as Grilamid L20base with a 50% concentration of an injection grade Nylon 12(Nanocomposite), as the outer layer. The three layers are delivered viaa highly polished spiral helicoid to a mandrel inserted into the dieopening and positioned flush with the die face or slightly protrudingunder pressure. The die has a circular outer ring and an inner plug,positioned so as to create a cylindrical tube of material. The outerring has an inner diameter of 0.042 inches, and the outer edge of theinner plug is spaced from the inner diameter of the outer ring by 0.100inches. The three materials are delivered to exit the die simultaneouslyto form a three layer tube. The middle tie layer does not use a meltpump to deliver material to the diehead, and the amount of material tobe delivered is controlled by the screw speed. The inner layer and theouter layer use a melt pump to deliver their respective materials to thedie head. On line ultrasonic gauging is used to measure the three layerthicknesses. The ultrasonic unit sends the information to the controlsystem, and the pump and screw speeds are automatically adjusted toattain the desired wall percentages. The ultrasonic gauge also measuresthe overall wall thickness and the control system translates thisinformation, and signals the puller to increase or decrease speed asnecessary. Supplied air is used to maintain a consistent inner diameter(i.d.) under control of the control system. The concentricity of thelayers is controlled by the control system using mechanical adjustmentcylinders with spring loaded pistons, in the head, that apply andrelease pressure to the ring which holds the die.

The plastic is melted in the extruders using three 1000 watt heaters setto maintain a temperature of 195° C. in the melt pool of the firstextruder and 201° C. in the second extruder. The die is also heated to atemperature of 210° C. by heaters. The control system monitors thetemperature settings of all three extruders. All parameters and outputscontrolled by the control system are recorded automatically. All datarecorded is stored securely and may not be altered. The control systemincludes software that records and interprets the capabilities of theprocess.

The blower speed and pulling mechanism are speed controlled in aclosed-loop manner. The speed of the puller may be changed as necessary,to consistently keep the overall wall thickness. The ultrasonic gaugesends the information to the control system and the signal is made tochange the speed. When a new tube is to be produced, the set points forthe blower and the pulling mechanism are reset by a synchronizationpulse. Once the tubing has passed through a surface blemish detector,only the good parts are kept via a blowoff setting controlled by thecontrol system. The bad parts (only the portion of the tube that was badplus 1 inch) are diverted to a scrap receptacle that is situated on ascale. The cutting sequence is triggered as often as necessary so thatgood parts are saved and bad parts are not. The control system recordsand tracks the bad material by weight. The synchronization along withreal time linespeed monitoring (a device that reports to the controlsystem) helps ensure a very precise, consistent length.

This tube may also be produced with multiple tapers. The tubespecifications are entered into the control system, and the ramps andtheir lengths are automatically set to realize the specification. Theultrasonic gauge provides real time information to the control system,and real time changes are made as necessary to maintain concise tapers.These tubes are also subjected to the blemish detection system. Thesynchronization sequence allows for only good parts to be saved, and badparts are separated.

One example of a resulting catheter produced according to the presentinvention may have the following dimensions and tolerances. The tubewith no taper would has an o.d. of 0.0253 inches, and an i.d. of 0.0176inches. The wall percentages is 15 percent on the tie layer and 42.5% onthe outer and inner layer. The tapered tube has a proximal o.d. of0.0253 inches with an i.d. of 0.0193 inches, and the distal end has ano.d. of 0.0226 inches, with an i.d. of 0.0176 inches. The layerpercentages are the same as the straight tube. Concentricity of thewalls is 0.0002 inch maximum difference. The i.d. and o.d. tolerancesare about ±0.0003 inches. The layer percentages is no more than about ±3percent.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, although many of the examples have been described with relationto the production of medical catheters, the systems and methodsdescribed could be used to produce any appropriate article (or articles)in a broad range of fields. Also, although a particular user interfacemay be illustrated in the embodiments above, the invention is capable ofoperating with all sorts of interfaces. Moreover, the particular devicesthat interface with the control system and the manner in which they areinterfaced can be modified according to the needs of the system.Accordingly, other embodiments are within the scope of the followingclaims.

1. An extrusion control system for use with one or more extruders,comprising: a data acquisition module in communication with one or moredata acquisition nodes that are associated with an extrusion process; acontrol module in communication with one or more control nodesassociated the extrusion process; and a synchronization signal generatorthat generates a synchronization signal for the one or more controlnodes to cause the one or more control nodes to adjust to apredetermined setting.
 2. The extrusion control system of claim 1,further comprising a part profile that corresponds to an extruded partto be produced by the one or more extruders.
 3. The extrusion controlsystem of claim 2, wherein the part profile comprises a representationof the outer diameter of the extruded part.
 4. The extrusion controlsystem of claim 3, wherein the part profile comprises a minimumspecified part profile and a maximum specified part profile.
 5. Theextrusion control system of claim 2, wherein the synchronization signalgenerator generates a synchronization signal at a substantiallyrepeating period.
 6. The extrusion control system of claim 5, whereinthe substantially repeating period is a function of the length of theextruded part.
 7. The extrusion control system of claim 6, wherein thesynchronization signal is generated for each part.
 8. The extrusioncontrol system of claim 2, further comprising a first event markerassociated with the part profile, whereby the synchronization signalgenerator generates a synchronization signal when the system encountersthe event marker.
 9. The extrusion control system of claim 8, whereinthe first event marker corresponds to the beginning of the part profile.10. The extrusion control system of claim 8, wherein the first eventmarker corresponds to the end of the part profile.
 11. The extrusioncontrol system of claim 2, wherein the data acquisition module and thecontrol module are each in communication with a computer that monitorsand controls the operation of the one or more extruders.
 12. Theextrusion control system of claim 11, further comprising a displayassociated with the computer that presents an image of the part profile.13. The extrusion control system of claim 1, wherein the synchronizationsignal generator communicates with each of the one or more control nodesover a dedicated communication channel.
 14. The extrusion control systemof claim 13, wherein the synchronization signal comprises asynchronization pulse.
 15. The extrusion control system of claim 1,wherein the synchronization signal generator communicates with each ofthe one or more control nodes over a shared communication medium. 16.The extrusion control system of claim 1, further comprising a velocitysensor that allows the velocity of an extruded article to be measured.17. The extrusion control system of claim 1, wherein a data acquisitionnode comprises a laser gauge.
 18. The extrusion control system of claim17, wherein the laser gauge acquires data relating to the outsidediameter of an extruded article produced by the extrusion process. 19.The extrusion control system of claim 1, wherein the control module isin communication with a PID controller associated with a variable speeddrive for the extruder, and the synchronization signal causes the PIDcontroller to return to a preset speed.
 20. The extrusion control systemof claim 1, wherein the control module carries out a PID controlsequence after the synchronization signal generator generates thesynchronization signal.
 21. The extrusion control system of claim 1,wherein the control module communicates with control nodes on more thanone extruder.
 22. The extrusion control system of claim 21, wherein thecontrol module causes a switchover form a first material in a firstextruder to a second material in a second extruder.
 23. The extrusioncontrol system of claim 1, wherein the control module is incommunication with a sizing air device controller associated with anextruder, and the synchronization signal causes the sizing air devicecontroller to set to a predetermined value.
 24. The extrusion controlsystem of claim 1, further comprising a reporting module that providesdata acquired by the data acquisition modules.
 25. A method of producingan extruded article comprised of a plurality of extruded parts,comprising: defining a part profile; associating a plurality of controlparameters with the part profile, wherein each control parameter has aninitial value; producing a first extruded part using the plurality ofcontrol parameters in a closed-loop control system; resetting each ofthe plurality of control parameters to its initial value; producing asecond extruded part using the plurality of control parameters in aclosed-loop control system.
 26. The method of claim 25, wherein the stepof resetting comprises sending a synchronization signal to a pluralityof control nodes.
 27. The method of claim 25, wherein thesynchronization signal is a pulse.
 28. The method of claim 25, whereinthe synchronization signal is transmitted on a dedicated communicationpath.
 29. The method of claim 25, wherein the synchronization signal issent after the first extruded part is produced and before the secondextruded part is produced.
 30. An extruded article, comprising: aplurality of extruded parts; a plurality of material transitions,wherein each part contains at least one material transition; and whereinthe material transitions are each shorter than 0.25 inches in extrudedlength.
 31. The extruded article of claim 30, wherein the plurality ofextruded parts comprises more than 30 parts.
 32. The extruded article ofclaim 30, wherein the plurality of extruded parts comprises more than 50parts.
 33. A plurality of extruded parts produced as part of asubstantially continuous extrusion process, comprising: a first sectionon each of the plurality of extruded parts having a constant outsidediameter; a second section on each of the plurality of extruded partshaving an increasing outside diameter; wherein the outside diameter ofthe first section of each of the plurality of extruded parts issubstantially identical to the outside diameter of the first section ofeach of the other extruded parts; and wherein the outside diameter alongthe second section of each of the plurality of extruded parts issubstantially identical to the outside diameter along the second sectionof each of the other extruded parts.
 34. The plurality of extruded partsof claim 33, wherein the outside diameter of the first section of thefirst extruded part differs from the outside diameter of the firstsection of any other of the plurality of parts by no more than 0.0010.35. The plurality of extruded parts of claim 33, wherein the outsidediameter of the first section of the first extruded part differs fromthe outside diameter of the first section of any other of the pluralityof parts by no more than 0.0005″.
 36. A extruded catheter, comprising: acatheter tip made of a first plastic material; a balloon having anexpanding portion, a middle portion, and a contracting portion; and acatheter shaft defining a lumen connected to the contracting portion,wherein the catheter shaft has a transition zone smaller than 0.25inches in which the catheter shaft transitions from the first plasticmaterial to a second plastic material.